I was thinking about the blue window stuff and was trying to remember when Skellebro seen it for the first time ... and it was definitely during the time period covered by the manga ... in other words Skellebro v1 ( the one that served Succubus during the demon invasion ) either did not see it or didn't recalled seeing it. And now , in this timelime specifically we get intel that Rubia can see her own window ...
Now a question: the other timelines Rubia did see the window or not? I think it is legitimate to ask that because of what I said above: If Skellebro v1 did not have a window , maybe Rubia v1 and v2 also did not have it as well. Maybe the assimilation rate we see is not a measure of anything related specifically to Skellebro, but about the number of blue window holders and their divergent actions from whatever 100% assimilation rate means? ( using Isaac theory, the more NPC ... err ,"residents", are replaced with playe ... err, "guests" , more the scenario will be divergent from whatever the original all NPC ...err, "residents", timeline would live in originally )
In other words, player 1 entered in here in timeline 2 ( the one with Rena, the slime guy, the biker nun, Madame ... ) controlling Skellebro and player 2 joined in timeline 3 ( better said, 4 , if we count the brief stint of Rubia as governor of Erast ) controlling Rubia in Co-op, after player 1 died in a dead end scenario vs Madame. And our point of view in this narrative is from the point of view of what would be Skellebro NPC ...
Wno knows , it might even be true
